1. Field of the Invention
Surface weirs have long had widespread use as a means of controlling or measuring liquid flow rates. They are used in devices to skim liquid surfaces of unwanted materials and also in apparatus for separation of liquids having different densities. Chemical manufacturing processes, water treatment process, waste treatment processes and water pollution cleanup operations all use separating, flow regulating or skimming devices. It is to this broad area of application that the invention is directed.
2. Description of the Prior Art
Most of the weir devices in use as separating, regulating or skimming apparatus are somewhat limited in operation and application. The weir itself is generally of a segmental gate design with a limited control surfaces and it may or may not be buoyant or floatable. Where the weir itself is not buoyant, liquid operating levels, relative to the weir, must remain relatively constant if a continuous rate of flow is to be maintained. When the weir is buoyant or floatable, it must be responsive to liquid level changes on one side or the other of the weir itself. Most devices respond to the downstream liquid level. The weirs which are manually adjustable require frequent monitoring and the ones which are automatically controlled are complex and somewhat complicated. These weirs have a relatively narrow operating range or capacity and they are designed for either a fixed or a floating platform installation--but generally not both.
Weirs which are mounted on, or as part of, a floating platform are usually utilized as skimming devices in sewage treatment ponds, swimming pools or pollution cleanup operations. Flow across the weir is generally withdrawn from a sump on a suction basis either as a siphon or by mechanical means. A chronic problem for floating skimmer operations is loss of prime in the sump, caused either by flow interruptions across the weir itself as a result of disturbances to the unit or to the liquid surface, or as a result of changes in the suction flow rate.
The loss of prime in the sump causes a corresponding increase in the buoyancy of the entire skimmer apparatus. The increase in buoyancy and freeboard further restricts or stops the flow across the weir edge. A loss of siphon or ingestion of air into the suction system also results from the loss of prime. Once the prime is lost, the unit is inoperable until the prime is restored. Air trapped in the suction system, as a result of the prime interruption, must also be purged to restore flow. Automatically controlled devices to correct this problem are sophisticated and expensive. Corrective responses to disturbances and flow changes must be immediate.